Many studies have documented gene flow from transgenic crops into nearby crop fields. To identify factors that enhance unwanted gene flow, we monitored commercial fields of non-Bt cotton grown for seed in Arizona. We measured density of pollinators and adventitious transgenic Bt plants in the non-Bt seed production fields, and obtained GIS maps of Bt and non-Bt cotton fields surrounding seed production fields. We quantified gene flow in seed production fields, as evidenced by seeds that contained the Bt toxin Cry1Ac, and used spatial statistics and multiple logistic regression to draw connections between landscape attributes and gene flow.  

Results/Conclusions

Pollen-mediated gene flow was best explained by abundance of Bt cotton fields within a distance of 750m from seed production fields, density of flower foraging honeybees, and density of adventitious Bt plants in the non-Bt cotton fields. When present, adventitious Bt plants appeared to cause sufficient outcrossing of surrounding non-Bt plants to overwhelm the effects of nearby Bt cotton fields on outcrossing. Our study shows that multiple sources of transgene flow and their interactions must be considered simultaneously to understand and limit transgene flow in seed production.